The present invention relates generally to a method for monitoring shaft doors of an elevator installation.
Elevator installations usually include shaft doors that in closed state separate, on each floor, the elevator shaft from the adjoining spaces. In the case of elevator installations of the conventional kind, the load receiving means (elevator car) is also equipped with a door, which is termed a car door and which moves together with the elevator car from floor to floor. The opening and closing of the car doors is normally effected, during stopping of the elevator car at a floor, by a car door drive controlled by an elevator control. In that case the car door panels are coupled with the respectively corresponding shaft door panels so that the shaft door panels accompany the movement of the car door panels.
For the safety of users of the elevator installation and passers-by in the building it is of great importance that a shaft door should be open only if the elevator car stops at the associated floor. In order to ensure this, there is monitored, apart from other elevator parameters, the positions not only of the shaft door panels, but also of the shaft door locks locking the shaft door panels. This usually takes place in such a manner that each shaft door lock is associated with a safety contact which forms a part of an electrical safety circuit and interrupts this circuit in the case of incorrect locking of the shaft door panels.
Such safety circuits, which in the case of high buildings can comprise a serial connection of more than twenty safety contacts, are known as one of the principal causes of disturbances in elevator operation. Due to corrosion and contamination the contact resistance of the individual safety contacts increases in a relatively short time, which in the case of serial connection of several contacts causes such a high voltage decay that the safety circuit system switches off the elevator even when the doors are correctly closed. Moreover, the investigation to find an individual defective safety contact or to find an incorrectly closed shaft door in a building with many floors is extremely time-consuming.
Additional problems with the monitoring of shaft doors have resulted in recent years from persons who enter the elevator shaft in unauthorized manner, whether it be to undertake highly risky “elevator surfing” or to block the elevator car between two floors and threaten or rob elevator passengers.
A shaft door monitoring system for a conventional elevator installation, which is to eliminate the above-described problems, is known from the U.S. Pat. No. 5,644,111. In this shaft door monitoring system, a contactlessly acting sensor in the form of a photoelectric detector with emitter and receiver is installed on each floor at the shaft wall opposite the shaft door. The light beam of the sensor is directed to the closing edge region of the closed shaft door panel and is reflected by the shaft door panel insofar as the shaft door panel is completely closed and the elevator car is not disposed between the sensor and the shaft door. If the shaft door panel is not completely closed and the elevator car is not in the region of the sensor, then the light beam exits into the elevator lobby from where it is no longer reflected in sufficient strength, so that the receiver of the photoelectric detector can register this state. A corresponding item of information is passed on to the elevator control, which stops the elevator and triggers suitable alarm signals (sirens, flashing light at the floor, etc.). If the elevator car is disposed at the floor with the unclosed shaft door, then the light beam of the sensor is reflected by the rear car wall so that the sensor correctly does not detect an impermissible state.
Such a shaft door monitoring system does indeed solve some of the afore-described problems, but has certain deficiencies.
The problem with the susceptibility of the safety circuit to disturbance is not eliminated by the disclosed solution, since such obviously exists unchanged and monitors, additionally to the photoelectric detectors, whether the shaft doors are closed and locked. Moreover, reliable functioning of the photoelectric detectors could be prejudiced by the fact that a person or an object disposed in front of the door gap of an incompletely closed shaft door reflects the light beam issuing into the elevator lobby and thus renders the monitoring system ineffective. In addition, a strong light source in the elevator lobby could impair reliable functioning of the sensor in the case of an incompletely closed shaft door. Further disadvantages result from the fact that a contact-free sensor has to be present at each floor. In the case of buildings with a large number of floors, an increased susceptibility to disturbance is inevitably caused by the correspondingly large number of sensors and the cost of periodic checking of the sensors is considerable. In addition, high costs arise for acquisition and installation of this multiplicity of sensors.